The fabrication of ribbons of glass by a float-glass technique is well-known. It is also known that cooling devices are utilized with the float-glass installation for purposes of cooling the glass ribbon either exclusively or preferably within the vicinity of its mid-region. Cooling within the mid-region has been found to be necessary to eliminate or substantially reduce any temperature gradient as may occur across the ribbon of glass and which otherwise may prevent the formation of a uniform ribbon of glass. To this end, cooling is carried out within the region which is less effected by heat losses through the sidewalls of the installation.
One cooling apparatus that is known in the prior art is formed by a container arranged centrally over the ribbon of glass. The container is of fixed dimension and includes a number of connecting lines which extend outwardly from the container through the sidewalls of the float-glass installation for purposes of circulating refrigerant through the container. Another known technique in cooling the ribbon of glass contemplates the penetration of the float-glass installation by a plurality of pipes extending entirely across the enclosed space from one sidewall to the other. Each pipe provides a path for circulating refrigerant. Also, it is known in the prior art to extend a plurality of pairs of pipes through a sidewall of a float-glass installation in a manner that the paired pipes, supported in cantilever fashion, are located above the ribbon of glass. The paired pipes may extend into the space above the ribbon of glass and molten bath from one or both sidewalls, as described in German Patent Specification No. 1 596 430.
In each of the prior art, the cooling pipes or the connecting lines to the cooling container providing a conduit for cooling material extend over the marginal regions of the ribbon of glass, regions which heretofore have been discussed as being more effected by heat loss through the sidewalls of the installation than the mid-region of the ribbon. Therefore, to obviate any cooling to the marginal regions, regions where cooling normally is not desired, the cooling pipes and connecting lines generally have been enclosed by a thermal insulation barrier in the form of a layer of insulating material, such as asbestos. In the prior art, the thermal insulation barrier is secured in place.
It has been found that securement of a thermal insulation barrier either on the cooling pipes or connecting lines occasionally may be detrimental to the successful implementation of the float-glass procedure. Thus, if the width of the ribbon of glass to be produced either is increased or decreased from that width of ribbon normally acted upon, then it may be that the length of the region along the cooling pipes or connecting lines provided with thermal insulation barrier either is too short or too long for the new condition. Also, in the prior art float-glass installations including a plurality of pairs of pipes which extend into the space above the ribbon of glass and molten bath, it may be that the pairs of pipes extend too far or do not extend far enough into the space for the new conditions. In this connection, the pairs of pipes either must be extended further into the space or retracted from the space. However, such movement results in movement or shift of the transition point between the cooling zone and the insulated zone. Such movement or shift of the transition point may also result in undesirable side effects. The undesirability of a cooling container of fixed dimension is even more pronounced as the width of the ribbon of glass or product is changed.
The present invention is directed to cooling apparatus which overcomes the problems and disadvantages of the prior art both discussed and as known to exist in the prior art. In general terms the present invention is directed to cooling apparatus comprised of conduit means for circulating a flow of cooling medium for cooling a ribbon of glass and insulation means disposed as a sleeve about and secured to the conduit means in a manner that the position of the transition point, and in fact a transition zone between a cooling region and a heat-insulated region is capable of change in location. Thus, a ribbon of glass of any particular width as may be produced within the float-glass installation may be cooled within the region of its axis to eliminate or substantially eliminate detrimental temperature gradients across the ribbon from the region of the axis outward toward its edges.